1. Field of the Invention
The present invention relates to a method for producing ionones or irones, or n-derivatives thereof, through the thermal rearrangement of certain novel propargylic alcohols. This invention also relates to such starting material propargylic alcohols.
2. Description of the Prior Art
The rearrangement of a propargylic alcohol to an unsaturated ketone under the influence of heat is generally known as the "Oxy-Cope rearrangement". However, the particular propargylic alcohols which are used in the present invention have not been subjected to an Oxy-Cope rearrangement, nor it is known that ionones and irones can be produced by this reaction. Briefly, the prior art relevant to an Oxy-Cope rearrangement reaction will now be reviewed. "Oxy-Cope rearrangement" is a term which was coined by J. A. Berson et al who studied this reaction with cyclic compounds [J. Am. Chem. Soc., 86, 5017 and 5019 (1964)]. Later, A. Viola et al studied the reaction of acyclic compounds in gaseous phase [J. Am. Chem. Soc., 87, 1150 (1965)]. Thereafter, a number of workers did theoretical and applied research on this reaction. However, as far as propargylic alcohols and their uses are concerned, only A. Viola et al [J. Am. Chem. Soc., 92, 2404 (1970] are known to have utilized this reaction. They obtained the unsaturated aldehyde ##STR2## by heating 5-hexen-1-yn-3-ol ##STR3## in a gaseous phase at 350.degree. to 390.degree. C.
Ionone has heretofore been commercially produced by cyclizing pseudoionone, which is obtained by the condensation of citral with acetone, or the reaction of dehydrolinalool with ethyl acetoacetate or diketene involving Carroll rearrangement, under the influence of a comparatively large amount of acid such as sulfuric acid or phosphoric acid [cf. U.S. Pat. Nos. 3,480,677 and 3,886,215, for example]. The reaction may be illustrated by the following scheme. ##STR4## In the above formula of ionone, the dotted lines represent a double bond in one or the other of the indicated positions. Irone is obtained by using 3,6,7-trimethyl-2,6-octadien-1-al in lieu of citral in the above reaction, or 3,6,7-trimethyl-1-octyn-6-en-3-ol in lieu of dehydrolinalool in the above reaction. The production of ionones or irones via the cyclization of pseudoionones or pseudoirones presents the problem of reactor corrosion due to the use of a comparatively large amount of acidic cyclizing agent. It is also not easy to dispose of the acid-containing waste solution.
Alkyl-substituted ionones such as methylionone are produced by condensing an alkyl-substituted acetone, e.g., methyl ethyl ketone with citral and subsequently cyclizing the reaction product. Of course, the products are mixtures of normal- and iso-alkyl-substituted ionones [cf. U.S. Pat. No. 2,877,271, for example]. The reactions may be illustrated as follows: ##STR5## (wherein R is a lower alkyl group)
Another prior art method for producing ionone commences with 2,6,6-trimethylcyclohexanone and comprises a combination of ethynylation reaction, dehydration reaction and Grignard reaction [U.S. Pat. No. 3,886,215 and J. American Chemical Society, 71, 4136 (1949)]. ##STR6## The above method is of little practical value because of the problems that [1] the starting material 2,6,6-trimethylcyclohexanone is not readily available, [2] the dehydration reaction of the ethynylation product of said cyclohexanone is low in selectivity and [3] the process involves a fairly large number of steps.